Support defining console variables with var consoleVar = someValue syntax

Support defining console variables with var consoleVar = someValue syntax

rename $var to $consoleVariables

move detection of JS console logic to .dart code from .js code
See https://codereview.chromium.org/24989007/ for the matching Blink change.

BUG=
R=blois@google.com, vsm@google.com

Committed: https://code.google.com/p/dart/source/detail?r=28243

[Jacob, 2013-10-01 18:12:39]

This CL goes along with 
https://codereview.chromium.org/24989007
to land true Dartium REPL support.

We had to move checking for _CONSOLE_API_SUPPORT_HEADER
out of DartDebugHooks.js as that line is now also passed in when not paused at a
breakpoint.
Switching to support

var x = foo

syntax in the repl isn't directly related to 
https://codereview.chromium.org/24989007
but is reflected by the test cases part of that CL
and I believe is a requirement for publicly announcing repl support.
If this CL was more complex I would break those two issues out into their own
CLs.

[blois, 2013-10-02 18:09:41]

lgtm

[vsm, 2013-10-03 16:04:06]

lgtm

https://chromiumcodereview.appspot.com/25570002/diff/4001/tools/dom/src/nativ...
File tools/dom/src/native_DOMImplementation.dart (right):

https://chromiumcodereview.appspot.com/25570002/diff/4001/tools/dom/src/nativ...
tools/dom/src/native_DOMImplementation.dart:247: // TODO(jacobr): remove the
parentheses around the expresson once
s/expresson/expression/

https://chromiumcodereview.appspot.com/25570002/diff/4001/tools/dom/src/nativ...
tools/dom/src/native_DOMImplementation.dart:265: * Returns a list of
completitions to use if the reciever is o.
s/completitions/completions/
s/reciever/receiver/

[Jacob, 2013-10-03 20:40:18]

Committed patchset #2 manually as r28243 (presubmit successful).